Flywheel bicycles

[karl]

I have been thinking about building a bicycle with built-in flywheel to conserve kinetic energy.
It has been done before quite succesfully.
This is a video of the Kers bike:

The Raht racer uses a pedal powered flywheel to power an electric engine, they say it can go up to 70mph:

This guy does not use a flywheel, but has a pedal powered generator which generates enough electricity, even without flywheel to powers the engine:

The idea of having a flywheel rotating at high speeds between my legs is a bit scary.
A crazy idea which i came up with is designing a wheel with a built in flywheel, but i don,t know if it,s even remotely possible.
In theory this sounds ideal, but there is a technical problem i cannot get my head around:
It is relatively easy to set the flywheel in motion and disengage it from the hub when stopping, i get that concept
from a freewheel. But does anyone have a clue as how to re-engage the spinning flywheel to drive the hub?

 

[Captain Awesome]

But does anyone have a clue as how to re-engage the spinning flywheel to drive the hub?

Conical clutch of some type like a snowmobile uses? It's not like you could just drop it into a gear or have engagement pawls. It would be too abrupt and shave off momentum

 

[mikeeebikey]

A small centrifugal clutch!
Since you are already building a flywheel set up why not power a generator to charge a battery, then go with an electric hub???

 

[karl]

You are right about the centrifugal clutch, that,s what i figured after a few hours of studying clutches. The centrifugal clutch will be connected to the axle, and engage the flywheel when it starts rotating, so the axle and flywheel will alternately drive each other. The flywheel itself will be connected to the axle with bearings left and right so it will spin freely.
Something like that, if these sentences sound somewhat comprehensible..
As far as the electrical side, you are probably right but i am just starting to understand the mechanical side of the concept myself..
Gonna make a design in sketchup soon!

 

[Duchess]

You're only going to want to engage the flywheel to charge it up under braking as that's how it will work. For the drag it would create under pedaling it would really only work for accelerating after a stop. If that's what you're looking for, it should work well. If you're going to pair it with an electric motor, it could work as regenerative braking. If you used an overdrive ratio for the flywheel-motor drive, you'd probably get more out of it than just using no flywheel and a motor with a controller that allows regen braking, but the amount of energy you get back on a bike is not terribly significant and it's restricted by how much you can safely charge the battery at a time, so the potential benefits of the flywheel would be limited by the battery's C rating. Any time you convert energy, there's a loss, so it's a matter of managing how it's distributed by preference against the compromises of the system. There's also the weight you'd be carrying around at all times affecting the acceleration or hill climbing (the latter if the flywheel hasn't enough energy to assist). A pro cyclist can maintain in the ballpark of 250W for a sustained period. Apply that (or, realistically, less and subtract some more watts for conversion losses) to a generator charging a battery or even to run a motor directly and you can see that you're better off mechanically running the bike from just a motor and a battery like a traditional e-bike. Like regen braking through an electric motor, the KERS system works because of the large amount of energy a car carries under braking that can be converted or that can be generated by any surplus power the engine has when under less than 100% load. That's the flip side of a bicycle's incredible efficiency.

 

[Grant]

Insane

 

[horsefarmer]

And now this:
Gyrobus: The Flywheel-Powered Public Transportation
https://www.amusingplanet.com/2019/02/gyrobus-flywheel-powered-public.html

 

[karl]

¨You're only going to want to engage the flywheel to charge it up under braking as that's how it will work. For the drag it would create under pedaling it would really only work for accelerating after a stop¨

I want to engage the flywheel while accelerating after slowing down or braking, so the flywheel maintains its momentum or kinetic energy while braking and decelerating.
If the flywheel has a higher speed than the wheel it will drive the wheel, if not the wheel will power the flywheel.

¨There's also the weight you'd be carrying around at all times affecting the acceleration or hill climbing (the latter if the flywheel hasn't enough energy to assist)¨

This is about Maxwell von Stein,s flywheel bicycle who was awarded the Nicholas Stefano Prize for an outstanding mechanical engineering senior project to Maxwell von Stein:

¨The Flywheel Bicycle has a continuously variable transmission in the rear hub. This is linked to a 6.8 kilogram (15 lb) flywheel from a car engine mounted in the middle of the frame. When the cyclist wishes to slow down, such as when they're going down a hill or coming to a stop, they shift the transmission to maximize the flywheel-speed-to-bike-speed ratio. This "charges" the flywheel with kinetic energy - effectively a mechanical version of what happens in an EV where a battery stores the scavenged energy.

Once they want to accelerate or climb a hill, they do the opposite - they shift the transmission to minimize the ratio. This lets the energy stored in the flywheel drive the transmission, giving the bike and its rider a boost. In a ride where speeds vary between 20 and 24 kph (12.4 to 14.9 mph), the system is claimed to not only increase acceleration, but to also produce 10 percent in energy savings.¨

https://newatlas.com/flywheel-bicycle-regenerative-braking/19532/
https://blogs.scientificamerican.co...-and-other-student-engineer-inventions-video/
Something else but awesome cool Btw. this is how the Gyro-x works:

 

[Duchess]

I'm not sure if you posted that in refutation or agreement, but that's essentially what I'm saying. You'd charge the flywheel under braking so that you could use its captured energy to accelerate after. As for the follow up to the second quote, I'm not sure how they're related. It would depend on your topography, but what I meant by what I wrote is that if you have a lot of longer stretches of steady riding or long climbs, the flywheel will lose its energy and then it's just extra weight you're carrying at all times. Of course, if you're going to be doing a lot of slowing and accelerating, then you'd see a lot more benefit. The gear ratio thing is just a way to better utilize the potential of the flywheel. To take advantage of gearing by utilizing a gear set for the wheel's internal flywheel, which would have to be separate from the drive, although selectively mated via some kind of clutch, would be quite the engineering challenge here.

 

[karl]

The flywheel should be charged by accelerating, not by braking, and maintain it,s momentum while braking or slowing down.
As bicycles are constantly slowing down and accelerating, the benefits are larger then from accelerating after a stop alone.
Of course there is the added weight to be taken into account, which may outweigh the benefits while on a steep long climb, but i am not trying to design a tour de france bike,
just doing some thought experiments for now.
Another option could be to use a flywheel as an electric generator to power an electric motor,
then there would be no loss of energy due to friction or gravity while pedaling, as in the Raht Racer. But purely mechanical systems can also increase acceleration and produce up to 10 percent in energy saving as proven by Maxwell von Stein.

 

[Duchess]

I think we're using alternate definitions of charging. When I use "charging", I'm referring to spinning the flywheel up so that you can harvest its energy later, like with a battery.

The flywheel will also resist turning and leaning, though it will certainly be easy to keep you balance.